Thermoplastic large diameter pipe, principally polyethylene and polybutylene, are increasingly useful in the mining industry. It is used in the mining of coal, copper, molybdenum, phosphate and uranium for slurry, leaching, acid and caustic piping as well as fire, process and portable water lines. The new thermoplastic pipe, especially polyethylene and polybutylene, offer our country a light-weight and economical piping system for mining/energy production, but the thermoplastic pipe lengths are difficult to connect by the conventional butt fusion, or fragile makeshift coupling systems.
The lack of a reliably efficient fitting or coupling which may be readily connected and disconnected has hindered the use of plastic piping in the mining industry. For example, coal mining requires a mobile or portable piping system that allows a miner to take lengths of pipe underground where they are joined or coupled together. Butt fusion or thermal welding of thermoplastic pipe lengths provides a reliably effective coupling. However, lengths of pipe joined by butt fusion cannot be readily disconnected and the butt fusion process cannot be used in an underground mine because of the danger of accidentally igniting the coal dust or methane gas commonly found in mine shafts.
Polyethylene pipe provided with a convenient and reliable fitting for releasably coupling lengths together would make an ideal portable pipe line for an underground coal mine because it possesses the best properties available today with respect to resistance to corrosion, abrasion and impact and its low coefficient of friction. It is light-weight and easy to handle and is sufficiently flexible to be easily bent around corners. There is no scale build-up in plastic pipes such as occurs in steel piping with consequent spray nozzle plugging.
Today's modern mine will advance or grow several hundred feet each week, and as one section is worked out the pipe is moved to another location. A quick mechanical coupling is essential to efficient operation.
The energy requirements for manufacturing polyethylene pipe are only about one-third the energy requirements for making steel or aluminum piping. The increased use of thermoplastic piping to be made possible by the fitting of the present invention will be an energy saver as well as an energy producer.
At least one attempt has been made to use mechanical couplings for joining lengths of plastic pipe. Plastic Pipe Lines Division of M. L. Sheldon Plastics Corporation, 350 Lexington Avenue, New York, New York 10016 has provided special polyethylene adapters on lengths of high density polyethylene pipe, the polyethylene adapters being of the same polymer as the pipe and not having increased mechanical strength properties of the polymer at the connecting portion, but being circumferentially flanged to receive metallic couplings which releasably join lengths of the high density polyethylene pipe together. The polyethylene adapters are not grooved as are conventional metal pipe lengths, but the special abutting flanges on adjoining pipe lengths conform with a metallic coupling such as made by Victaulic Company of America, 3100 Hamilton Boulevard, South Plainfield, New Jersey 07080. This metallic coupling is in two sections and each section is wide enough to fit over the abutting flanges on adjoining pipe lengths. After both sections of the Victaulic coupling have been assembled on the flanges, the two sections are joined by tightening two bolts, one on each side of the pipe. These connections have proven generally satisfactory in low pressure lines such as gravity service provided in decant lines, but the Sheldon connection is not understood to be effective in coupling lengths of plastic pipe subjected to the high pressures sometimes required in pipe lines.